Small spindles are used mainly in light-load machining such as working on aluminum.
In recent years, an increasing number of small spindles is of a type where a motor 2 is incorporated in a housing 1 as shown in FIG. 6 (Patent Literature 1) for a purpose of compactness. In FIG. 6, a symbol W represents a workpiece.
Motor-incorporating-spindle of this kind often makes use of angular ball bearings as ball bearings 3 since high speed operation is required.